AU3679299A - Method and apparatus for locating obstructions in a pipeline - Google Patents

Description

1

AUSTRALIA

Patents Act 1990 Complete Specification For A Standard Patent METHOD AND APPARATUS FOR LOCATING OBSTRUCTIONS

IN

A PIPELINE The following statement is a full description of this invention, including the best method of performing it known to me: 5 This invention relates to determining the location of obstructions within a pipeline.

One example of such an obstruction is a moveable device commonly referred to as a pig. Pigs are often used for batching products, cleaning, gauging, sealing sections of too: .pipeline, internal inspection, and the like. Those pigs may become stuck within the 10 pipeline due to blockages, damaged sections of pipeline or loss of propulsion of the propelling medium. It is then necessary to determine the location of the pig to be able t.o to rectify the problem.

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Previous acoustic methods of locating obstructions are limited to short distances of a 15 few hundred metres. Such acoustic methods are crude and use audible echoes of sounds produced by means such as impacting the pipes, firing an explosive charge or by persons making a noise like clapping or shouting. Where the obstruction is a pig, a transmitter placed on the pig emits an electromagnetic signal that can be sensed by a detector on the outside of the pipeline. This method has problems due to stray interference or difficulty in accessing the pipeline where the pipeline was deeply buried or under water. The limited lifespan of the transmitter limits their use in long distance pipelines.

The invention resides in a method for determining the location of an obstruction within a pipeline containing a fluid medium, the method including the steps of detecting a first acoustic signal, detecting a second acoustic signal, and determining the location of the obstruction from said detection of the first and second acoustic j g 2 signals wherein the first acoustic signal is created by a flow fluctuation of the fluid medium, and propagates through the fluid.

The invention also resides in apparatus for determining the location of an obstruction within a pipeline containing a fluid medium including means for detecting a first acoustic signal, means for detecting a second acoustic signal, and means for determining the location of said obstruction from said first and second acoustic signals, wherein said first acoustic signal is created by a flow fluctuation of the fluid medium, and propagates through the fluid.

**Fluctuations in the flow can be created for example, by opening and closing a valve providing a rapid flow of material to or from the pipeline, or a change of phase of the fluid medium. Changes in flow can also be created in a region substantially adjacent the obstruction, for example when a moving obstruction stops or starts or when it 15 enters an ovalised or damaged section of the pipeline where the fluid can bypass the edges of the obstruction. Where the obstruction is a pig, it may be provided with means to permit fluid to rapidly transfer around or through the pig to produce a fluctuation in the flow. These flow changes are localised and form an acoustic signal that propagates through the fluid between the obstruction and the detecting means.

In the case where the first acoustic signal is created by or adjacent to the obstruction, the first acoustic signal may be detected on a first side of the obstruction and the second acoustic signal may be detected on a second side of the obstruction opposite the first side.

Signals of the type produced in the manner herein described are typically of low frequency and large amplitude and are capable of being detected at large distances from the source. Amplitudes greater than 0.1 kPa and frequencies less than 100 Hz are preferred for long distance applications, however the amplitude and frequency used will depend upon the length and diameter of the pipeline and the attenuation of the fluid medium.

S2 3 The invention will now be described by way of example only with reference to the accompanying figures in which: Fig 1 shows a first schematic form of the invention; Fig 2 shows a second schematic form of the invention having two pressure transducers; and Fig 3 shows a third schematic form of the invention including a fluid reservoir.

The invention is described with particular reference to determining the location of pigs within pipelines but it is intended that the invention can be used for any obstruction, or "°partial obstruction within a pipeline, provided the obstruction can either create or substantially reflect an acoustic signal.

Fig 1 shows a pipeline 11 terminated at an end 12 that may be open, closed or partially closed. The pipeline 11 contains a fluid medium that may be a liquid or gas or a mixture of gas and liquid phases.

A moving obstruction 10, such as a pig, will stop and start and change velocity as it 0. °progresses along the pipeline. Each change of velocity causes a flow fluctuation to be 0: 20 created in front of and behind the obstruction that propagates away from the 0. 0: obstruction at the acoustic velocity of the medium. Flow fluctuations will also be created when the obstruction enters a section of pipeline having a differing crosssection that allows fluid to bypass the obstruction thereby changing the fluid flow. In addition pigs travelling the pipeline may be provided with a high flow valve remotely operable by a radio, magnetic, electromagnetic or acoustic signal. When open, the valve allows fluid to pass rapidly around or through the pig. When the valve is operated, either by opening or closing, the flow conditions in the region of the pig are suddenly changed. The sudden change creates a flow fluctuation both in front of and behind the pig.

These flow fluctuations are created as a localised signal in the region of the obstruction and propagate as acoustic signals along the pipeline 11, echoing between 11 K ID F'~ a 4 the ends of the pipeline and the obstruction. Pressure transducers 20 are disposed in the pipeline 11 to detect the acoustic signals.

The transducers 20 are preferably placed in a branch connection of the pipeline 11 (not shown) such that they do not impede the passage of a pig or any other obstruction travelling through the pipeline. The transducers are preferably located near the end of the pipeline. In order to locate the obstruction with a reasonable degree of accuracy the transducer is capable of detecting signals having a frequency less than 100 Hz .i preferably less than 10 Hz and more preferably as low as 0.03 Hz. For detecting weak 10 signals the transducer has a sensitivity of 1 Pa or better but this can be as high as 500 to 1000 Pa for higher signal strengths. Pressure transducers with the above properties are widely available commercially. In operation, the pressure transducer 20 is preferably AC coupled though DC coupling can be used in conjunction with high pass filtering to remove the DC component.

As shown in Fig 1, the pressure transducer 20 is connected to a processing unit 22.

The processing unit receives the output of the pressure transducer(s) •••corresponding to detection of the first and second acoustic signals, calculates the location of the obstruction and displays the results on a display device 32 such as a 20 screen or printer.

In a first embodiment described in Fig 1, a single transducer 20 is placed at or near the end of the pipeline 11. The transducer 20 receives the acoustic signal created near the obstruction After a time delay, the transducer 20 detects an echo of the first acoustic signal. The echo will have travelled from the end of the pipeline to the obstruction to be reflected, and then travelled again to the transducer. Therefore the time delay between the detection of the first signal and its echo will be indicative of the distance to the obstruction.

ILIZZI VVT- Visual observation of the outputs of the pressure transducer 20 may be used to determine the time delay between the first signal and the echo. The time delay and the acoustic velocity of the medium can then be used to calculate the distance to the obstruction using well known acoustic theory. More preferably, and as shown in Fig 1, the output of the pressure transducer is received by the processor 22 which then calculates the location of the obstruction. The processor 22 also receives the outputs from supplementary transducers 25. These transducers can provide additional information such as the temperature, static pressure and flow rate of the fluid medium within the pipeline. Other parameters such as pipe diameter, wall thickness, pipe 10 elastic properties, fluid type and fluid properties such as density and compressibility .oo ~may be provided to the processor 22 through a user interface 30. These additional parameters allow the processor 22 to make a dynamic calculation of the acoustic velocity of the medium, increasing the accuracy of the obstruction location calculation.

To ensure that the echo of the signal is correctly identified from all other spurious "noise signals, the processor uses the first acoustic signal, the attenuation and .dispersive characteristic of the pipeline, and the transducer response characteristics to predict an echo. The characteristics of the predicted echo, such as amplitude and :20 shape, will depend on the time elapsed between detection of the first signal and detection of the echo. This elapsed time is representative of the distance travelled by the echo signal through the fluid and can therefore be used to predict the amount of signal attenuation and dispersion When a second acoustic signal is detected, an echo of the first acoustic signal is predicted and compared to the detected signal. The second signal is deemed to be the actual echo of the first signal if it correlates with the predicted echo with a predetermined degree of similarity. The time delay between the first signal and its echo is then combined with the acoustic velocity of the fluid to calculate the location of the obstruction.

Further refinement of the acoustic signals can be achieved using known signal processing techniques.

h 6 An alternative approach to locating the obstruction is shown in Fig 2 where a first pressure transducer 20a is disposed at a first end of the pipeline and a second pressure transducer 20b is placed at a second end of the pipeline opposite the first end.

Acoustic pressure fluctuations created by or near to the obstruction propagate forward and backward of the obstruction towards the respective transducers 20a, 20b. The time delay between the detection of the forward and backward propagating signals directly relates to the distance of the obstruction from the midpoint between the two transducers.

S: 10 Under static equilibrium conditions, the distance of the obstruction from the midpoint is equal to half the time delay multiplied by the acoustic velocity of the fluid. More •realistically, the acoustic velocity will differ on either side of the obstruction due to S C differences in temperature, pressure, density, the direction of flow relative to the propagation direction of the signal, etc. These factors are taken into consideration by 15 the processor 22 when calculating the location of the obstruction.

In a further embodiment described with reference to Fig 3, fluctuations in the flow may be actively created. Fig 3 shows the pipeline 11 being connected to a reservoir containing a fluid at a pressure substantially different to the pressure in the pipeline 20 11. The reservoir may be active such as compressor, pump or other device capable of supplying fluid of different pressure. Alternatively the reservoir may be the atmosphere. A valve 31 disposed between the pipeline and the reservoir controls fluid flow between the pipeline 11 and the reservoir 30. When the valve 31 is opened, there is a flow of fluid from the pipeline to the reservoir or vice versa depending on the direction of the pressure gradient. This sudden flow creates a localised low frequency acoustic pressure fluctuation that propagates along the pipeline to be reflected by the obstruction 10. The amplitude of the acoustic signal will depend on the magnitude of the pressure gradient from the pipeline to the reservoir and the size of the valve 31.

The higher the pressure gradient between the pipeline 11 and the reservoir 30, and the larger the valve 31, the more fluid that is transferred between the pipeline and the reservoir and the larger the amplitude of the acoustic signal created. The acoustic signal is detected by a pressure transducer 20 firstly as an outgoing signal and again A 7 after it has been reflected by the obstruction. The location of the obstruction is then calculated in the manner previously described. This method is particularly useful in the detection and location of stationery obstructions such as blockages, water pockets, damaged sections of pipe, stuck pigs etc., though it can also be used in locating moving obstructions of the type described above.

As shown in Fig 1 the output of the processing unit 22 is displayed on a display unit 32. The display unit 32 may be a screen or a printer or any other device for transfer of .i information to persons. The display unit 32 may be the same unit as the input unit 10 The method of transfer from the processing unit 22 to the display unit 32 may be by •direct means such as but not limited to electric wires or optical fibres or by indirect °means such as radio, infra red, acoustic, or optical. The location of the processing unit S22 and the display unit 32 may be close to or remote from each other. The output will include the location of the pig and may also include additional information such as the 15 pig's velocity and an indication of the level of accuracy of the calculations. The output may also include the location and size of other obstructions in the pipeline.

The output information may be stored within the processing unit 22 for later retrieval.

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The pressure transducers or the processing unit may incorporate filters to remove signals not attributable to the pig or obstruction.

While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (24)

1. A method for determining the location of an obstruction within a pipeline containing a fluid medium, the method including the steps of detecting a first acoustic signal, detecting a second acoustic signal, and determining the location of the obstruction from said detection of the first and second acoustic signals wherein the first acoustic signal is created by a flow fluctuation of the fluid medium, and propagates through the fluid. 10

2. A method according to claim 1 wherein the second acoustic signal is an echo of the first acoustic signal.

3. A method according to claim 1 wherein the first acoustic signal is created by a flow fluctuation of the fluid medium in a region substantially adjacent to the "15 obstruction.

4. A method according to claim 3 wherein the first acoustic signal is created by a So.o flow fluctuation of the fluid medium around or through the obstruction. 20

5. A method according to claim 3 wherein the flow fluctuation of the fluid medium is created by movement of the obstruction.

6. A method according to claim 1 or 2 further including the step of opening or closing a valve to create a change in the flow of the fluid medium within the pipeline.

7. A method according to claim 2 wherein the step of detecting the second acoustic signal includes the steps of using the first acoustic signal to predict an echo of the first acoustic signal, detecting a further acoustic signal and comparing said further signal with said predicted echo to determine if the further signal is the echo of the first acoustic signal.

8. A method according to claim 7 wherein the predicted echo is time dependent. 9

9. A method according to any one of claims 1, or 3 to 5 wherein said first acoustic signal is detected on a first side of said obstruction and said second acoustic signal is detected on a second side of said obstruction opposite said first side.

10. A method according to any preceding claim further including the step of calculating the acoustic velocity of the medium.

11. A method according to any preceding claim wherein the obstruction is a pig. 10

12. Apparatus for determining the location of an obstruction within a pipeline *containing a fluid medium including means for detecting a first acoustic signal, means for detecting a second acoustic signal, and means for determining the location of said °•.obstruction from said detection of the first and second acoustic signals, wherein said S°first acoustic signal is created by a change in flow of the fluid medium, and propagates 15 through the fluid.

13. Apparatus according to claim 12 wherein said means for detecting said °acoustic signals includes at least one pressure transducer. 20

14. Apparatus according to claim 13 wherein said at least one pressure transducer is capable of detecting signals having a frequency of less than 100 Hz.

Apparatus according to claim 14 wherein said at least one pressure transducer is capable of detecting signals having a frequency of less than 1 Hz.

16. Apparatus according to any one of claims 12 to 15 further including means for determining the acoustic velocity of the fluid within the pipeline.

17. Apparatus according to any one of claims 12 to 16 wherein the second acoustic signal is an echo of the first acoustic signal. A

18. Apparatus according to claim 17 further including means to predict an echo of the first acoustic signal and means for comparing said predicted echo with said second acoustic signal.

19. Apparatus according to claim 18 wherein said predicted echo is time dependent.

Apparatus according to any one of claims 12 to 16 wherein said means for detecting a first acoustic signal is located on a first side of the obstruction and said 10 means for detecting a second acoustic signal is located on a second side of said obstruction opposite said first side. o o

21. Apparatus according to any one of claims 12 to 19 further including valve means and means to open or close said valve means to create a fluctuation in the flow 15 of the fluid medium within the pipeline. a•

°22. Apparatus according to claim 21 wherein said valve means is located in a •o branch connection of the pipeline. a..a

23. Apparatus according to claim 21 or 22 further including a reservoir containing a fluid at a pressure substantially different to the pressure of the fluid within the pipeline, wherein said valve means is disposed between said pipeline and said reservoir.

24. A method for determining the location of an obstruction within a pipeline substantially as hereinbefore described with reference to the figures. 4 I1I Apparatus for determining the location of an obstruction within a pipeline substantially as hereinbefore described with reference to the figures. Dated this 25th day of June 1999 SAIPEM ASIA SDN BHD By their Patent Attorneys Halford Co